1. Field of the Invention
The present invention relates to an ink jet recording apparatus that discharges ink liquid to a recording medium for the formation of images thereon, and an ink jet recording method therefor. More particularly, the invention relates to an ink jet recording apparatus capable of attaining image recording in high quality and in high precision as well. The invention also relates to an ink jet recording method therefor.
2. Related Background Art
There have been widely known recording apparatuses that adopt the ink jet method whereby to form images by discharging ink to an recording medium. The ink jet recording method is of a recording method of a non-impact type. Therefore, its noises are smaller. Also, this method has an advantage, among others, that color images can be recorded easier by use of multiple color ink. With such advantages this method has, it becomes more popular increasingly and rapidly in recent years.
Also, for the ink jet method, the bubble jet method is known, in which electrothermal transducing elements (or heaters) that serve as means for discharging ink are used for the generation of air bubbles in ink by giving thermal energy generated by the electrothermal transducing elements to ink, and then, ink is discharged by the utilization of pressures exerted when air bubbles are generated. This bubble jet method makes it possible to arrange discharge ports in high density. Also, it has an advantage that apparatuses can be fabricated smaller, while performing image recording in higher resolution.
For the recording head of an ink jet method, the so-called multiple nozzle head is generally used. For this head, a plurality of ink discharge ports are arranged to enable plural ink droplets to be discharged at a time by use of recording elements provided for the recording head. In accordance with a recording head of the kind where a plurality of ink discharge ports are arranged, it is possible to form a plurality of dots at a time, and also, to shorten a period of time required for recording characters, images, and the like, which are formed by the collection of such dots. The recording speed of the apparatus can be enhanced as a whole accordingly.
However, it is known that there are the problems as given below with respect to recording by use of the multiple nozzle head described above.
In other words, for a recording head of the kind, it is difficult to manufacture a plurality of ink discharge ports and recording elements uniformly. As a result, recorded dots become uneven to a certain extent inevitably. For the multiple nozzle head, the amount of ink droplets and the discharging direction thereof are varied minutely, for example, due to the variation in the configuration of ink discharge ports and some other factors. Also, for the recording elements that discharge ink, its discharging performance is caused to vary, producing adverse effect upon discharged ink droplets. Also, in the bubble jet method described above, it is obvious that difference in the thermal energy generated by each of the individual recording elements makes the discharged ink droplets uneven.
As described above, unevenness occurs in the densities of recorded images if the sizes and densities of dots to be recorded are made uneven.
Particularly, for a recording apparatus of a serial type where recording is made while the recording head travels, the density unevenness takes place in the scanning of the recording head itself, at first, and then, the patterns of uneven density are formed repeatedly by a specific cycle due to the repeated scanning. Such patterns repeatedly made in a specific cycle can easily be observed visually by eyesight. In such case, therefore, the quality of recorded images and the like becomes remarkably inferior.
In order to reduce a density unevenness of the kind for the serial type recording apparatus, there has been proposed a method called a multiple scan where the feeding amount of a recording medium per scan of the recording head is made smaller than the recording width of the recording head, and an image in a given area is completed by the application of several scans. In accordance with this method, pixels on a given line in the scanning direction of the recording head are recorded by use of different discharge ports per scan. As a result, the density unevenness, which is characteristic of each discharge port of the ink jet head, is scattered in the recorded image, thus making its density unevenness less conspicuous.
Also, the defective discharge may take place in a particular ink discharge port of a multiple nozzle head and causes the generation of density unevenness in a recorded image or the discharge amount may vary due to the difference in use frequency of the discharge ports of the head. If use frequencies may differ greatly between each of them, the discharge amount of each discharge port varies. As a result, the density unevenness occurs in the recording image. Also, if the defective discharge takes place in a discharge port whose use frequency is particularly high, a problem arises to present more conspicuous streaks and density unevenness. Moreover, if it is arranged to form an image by the frequent use of only specific ink discharge ports, the use frequencies of ink discharge ports are greatly deviated among them. As a result, the probability of malfunction becomes higher for the discharge port whose use frequency is high. In other words, a problem is encountered that the life of a recording head becomes shorter eventually.
As means for solving these problems, a technique is disclosed in the specification of Japanese Patent Laid-Open Application No. 5-330083 wherein different discharge ports are used per pixel when forming pixels, and at the same time, the use frequencies of discharge ports are made uniform. In accordance with the disclosed technique, plural pixels contained in a given line in the main scanning direction are formed by the application of several scans, while a control is given so that plural pixels to be recorded are assigned to the corresponding discharge ports in a specific order per scan. In this way, the ink discharge ports are used uniformly, thus making it possible to prolong the life of the recording head. Also, even if defective discharge or other drawbacks take place in part of the discharge ports, the location of pixels that are not formed due to the defective discharges are scattered to make such pixels less conspicuous.
Now, the recording process will be described in accordance with such conventional method described above.
FIG. 5A is a view which schematically shows an ink jet type recording head 1 provided with a plurality of ink discharge ports (hereinafter, simply referred to as discharge ports). In FIG. 5A, 128 discharge ports are arranged in the direction from the upper part to the down part of the recording head 1. Here, the numbers marked with # are those indicating the positions of the discharge ports. For the recording head 1, the discharge ports #1 to #128 are provided.
Also, FIG. 5B is a view which illustrates the conventional recording method using the recording head 1. In FIG. 5B, an example is shown, in which an image is formed by scanning a given recording area with the recording head 1 four times. This example shows a recording method adopted for a so-called serial printer. The recording head 1 performs its recording while scanning in the main scanning direction indicated by a reference mark X, and the recording medium is fed in the sub-scanning direction indicated by a reference mark Y in FIG. 5B. This feeding of the recording medium should be good enough if only its operation is such that a recording medium shifts relatively with respect to the recording head. It may be possible to arrange so that a recording head is arranged to move in the sub-scanning direction while a recording medium is fixed. For the example shown in FIG. 5B, it is arranged that the recording head 1 moves relatively with respect to the recording medium in order to describe the recording positions of the recording head 1 on the recording medium.
Also, in FIG. 5B, reference numerals 1001, 1002, 1003, and 1004 designate the corresponding pixel arrays in the main scanning direction of the recording head 1, which are adjacent to each other in the arrangement direction of the discharge ports of the recording head 1, respectively.
In FIG. 5B, the pixel array 1001 is formed by ink droplets discharged from the discharge port numbers #97, #65, #33, and #1, respectively, at each of the four-time scans of the head, for example.
FIG. 6 is a view which illustrates an image formed on a recording sheet by the application of the recording method shown in FIGS. 5A and 5B. Each square represents the position where one pixel is formed. The squares indicated by slanted lines represent pixels formed by discharged ink. In FIG. 6, reference numerals 1001 to 1004 designate those pixel arrays shown in FIG. 5B. The numbers 1 to 16 shown in the lower part of FIG. 6 are line numbers that indicate recording positions in the main scanning direction of the recording head 1. In FIG. 6, only pixels designated by the numbers 1 to 16 are described for convenience's sake.
FIGS. 7A, 7B, 7C, and 7D represent each of the images formed by each scanning when the image shown in FIG. 6 is formed by the four-time scans as shown in FIG. 5B. Each of them corresponds to each image formed at the time of first to fourth scans, respectively. In FIGS. 7A, 7B, 7C and 7D, one square represents the position where one pixel is formed as in FIG. 6. The squares with slanted lines indicate pixels formed by discharged ink. The numbers with # shown on the right-hand side of each figure designate the discharge port numbers that correspond to the pixel positions in each of the pixel array. Also, the numbers shown in the lower part of each figure correspond to the line numbers represented in FIG. 6, respectively.
FIG. 8 is a view which illustrates the recorded pixels in the pixel array by use of the respective discharge ports per each scan in order to form them in such pixel array with attention given to the pixel array 1001 in the main scanning direction of the recording head 1.
In FIG. 8, one square represents the position where one pixel is formed as in FIG. 6 and FIG. 7A, 7B, 7C and 7D. The squares with slanted lines represent the pixels to be recorded by discharged ink. Also, each number with # and the number shown in the lower part of FIG. 8 are the same as those shown in FIG. 6 and FIGS. 7A, 7B, 7C and 7D.
On referring to FIG. 8, it is understandable that the discharge port numbers #1, #33, #65, and #97 are used twice, respectively, in order to form the pixel array 1001. In this way, with the sequential use of the discharge ports, it becomes possible to almost uniformalize the use frequencies of plural discharge ports, thus making the life of the recording head longer. At the same time, the deterioration of the image quality caused by defective discharges can be reduced, because the positions where pixels are not recorded are scattered even if defective discharges take place; hence obtaining good images.
However, in accordance with the conventional method described above, there is a need for the provision of drive data on discharge/non-discharge of ink per discharge port per scan using a mask pattern or the like. In this case, a large memory capacity is needed depending on the numbers of recording scans to be executed. For example, when one pixel array is formed using different discharge ports of N numbers by recording it with N times of scans on a given recording area, it is required to increase the required memory capacity N times the capacity provided for recording such given recording area by one time scan only. In other words, the total amount of data to be stored on the memory should be calculated as follows:
{(the numbers of discharge ports of a recording head).times.(pixel numbers per one pixel array).times.N} PA1 means for storing image data that stores image data in accordance with images to be recorded; PA1 means for storing context data that stores context data for controlling the recording/non-recording of the image data corresponding to the recording elements of the recording head; and PA1 calculating means for creating drive data indicating the recording/non-recording of the image data, at the same time, creating new context data corresponding to the recording elements in accordance with the image data to be stored on the means for storing image data, and the context data corresponding to the recording elements for recording the image data. PA1 providing context data for controlling the recording/non-recording of the image data corresponding to the recording elements of the recording head; PA1 creating drive data indicating the recording/non-recording of the image data in accordance with the image data and the context data corresponding to the recording elements that record the image data; and PA1 updating the context data for creating new context data corresponding to the recording elements in accordance with the image data, and the context data corresponding to the recording elements that record the image data. PA1 means for storing context data that stores the context data for controlling the recording/non-recording of the image data corresponding to the plural recording elements of the recording head; PA1 calculating means for creating drive data indicating the recording/non-recording of the image data, at the same time, creating new context data corresponding to the recording elements in accordance with the image data to be stored on the means for storing image data, and the context data corresponding to the recording elements for recording the image data; and PA1 head driving means for driving the plural recording elements of the recording head in accordance with the drive data. PA1 providing context data for controlling the recording/non-recording of the image data corresponding to the plural recording elements of the recording head; PA1 creating drive data indicating the recording/non-recording of the image data in accordance with the image data and the context data corresponding to the recording elements that record the image data; PA1 updating the context data for creating new context data corresponding to the recording elements in accordance with the image data, and the context data corresponding to the recording elements that record the image data; and PA1 recording by driving the plural recording elements of the recording head in accordance with the created drive data. PA1 image data storing means for storing the image data on images to be recorded, the image data being formed by data indicating pixels to be recorded or pixels not to be recorded; PA1 context data storing means for storing the context data for controlling the recording/non-recording of the image data corresponding to each of the plural discharge ports; PA1 calculating means for creating the drive data in accordance with the image data and the context data corresponding to the discharge ports that record the image data, at the same time, updating the context data in accordance with the data indicating the recording pixels of the image data; and PA1 setting means for setting the context data at its initial value per main scan by the main scanning means. PA1 providing image data formed by data indicating pixels to be recorded or pixels not to be recorded with respect to the image to be recorded; PA1 providing context data for controlling the recording/non-recording of the image data corresponding to each of the plural discharge ports; PA1 operating calculations to create the drive data in accordance with the image data and the context data corresponding to the discharge ports that record the image data, and at the same time, update the context data in accordance with the data indicating the recording pixels of the image data; and PA1 setting the context data at its initial value per main scan by main scanning means.
Such an increase of memory capacity creates a problem that the costs of an apparatus are inevitably increased as a whole.
Now, among known recording modes made available to recording apparatuses, there is one used for a high-speed recording in order to confirm the recorded result of prints or the like. This is generally called a draft mode. The draft mode is often applied to the case where it takes a long time to output the result of a regular recording, for example, and where such record should be made immediately or the output is made only for a document which is not very important. The draft mode is generally a method in which the pixels to be recorded are intermitted for recording. With the intermitted recording, it is implemented to make the recording speed faster. Among the intermitted patterns, there is a checker pattern, for example. Also, for the draft mode, the numbers of dots to be recorded are smaller than those of regular output. Therefore, this mode is also adopted for the purpose of curtailing ink consumption.
However, if an image is recorded in such draft mode while thinning the pixels to be recorded like a checker pattern, there is a fear that pixels are thinned unpreparedly, and that it tends to produce an image whose characters or the like cannot be recognized easily after all.